Reaction of a mercapto polymer with an nu-acyl polyimide of a polycarboxylic acid



United States Patent() REACTION OF A MERCAPTO POLYMER WITH AN POLYIMIDE OF A POLYCARBOXYLIC Robert D. Evans, Greenwich, Conn., and Milton J. Rhoad, Akron, Ohio, assignors, by mesne assignments, to The gloodyear Tire & Rubber Company, a corporation of No Drawing. Application September 11, 1952, Serial No. 309,133

3 Claims.

compounds are not generally applicable to the preparation of polythioesters from polymercapto compounds, particularly when polymers of high molecular weight are desired. One method for preparing linear polythioesters is described in U. S. Patent 2,510,567, according to which dimercaptans and dibasic acid chlorides arc condensed, with the elimination of hydrogen chloride. .ln that method, it is sometimes difficult to remove all of the hydrogen chloride, particularly in the later stages of the invention. Residual hydrogen chloride can at fect the color and stability of the polymer.

The present invention provides a means of producing polymers containing thioester linkages without the production of by-product hydrogen chloride.

According to the practice of the invention, a mercapto polymer is treated with an interlinking agent which is an N-acyl polyimide of a polycarboxylic acid, each of the carbonyl groups of the acyl radical being attached to the nitrogen atom of an imido radical. This class of compounds and their preparation are described in U. S. Patent 2,558,675 to Flory. The polymer can contain a plurality of mercapto radicals and, if desired, can also contain hydroXyl and/or amino radicals, which can also react with the interlinking agents. Amino radicals must contain a reactive hydrogen atom in order to enter into the interlinking process and are preferably primary amino. If the intermediate polymer contains only two reactive groups per molecule and the interlinking agent is bifunctional, the resulting high polymer will be linear, and hence thermoplastic. Cross-linked polymers are prepared by the use of a polymer and interlinking agent, one or both of which have more than two reactive groups.

The N-acyl. polyimides, when derived from dicarboxylic acids, may be called N-acyl bis imides and may be represented by the structural formula in which is an imido radical and is a diacyl radical. More broadly, when the polycarboxylic acid has x carboxyl groups, the products may be represented by the structural formula in which is an imido radical and is a polyacyl radical and x is 2 or more.

The interlinking reaction may proceed according to either or both of the following illustrative equations, in which N,N-terephthaloyl bis succinimide is shown as a typical N-acyl polyimide of a polycarboxylic acid.

The mechanism of the reaction is not known for certain and it is possible that both of the indicated types of reaction occur. In the equations, reaction has been shown on only one end of the polyimide. Similar reaction can and, in practice, does take place on both ends of the molecule.

The invention is broadly applicable to polymers containing one or more sulfhydryl groups. Thus the various superpolymeric polymethylene dithioterephthalates and dithioisophthalates derived from polymethylene dithiols containing from two to ten methylene groups, including the ethylene, trimethylene, tetramethylene, pentamethylene, hexarnethylene and decamethylene polythioesters and copolythioesters, are easily prepared by this method. Also, similar polythioesters derived from branched chain dithiols or dithiols containing either oxygen or sulfur atoms as integral parts of the chain separating the two mercapto groups can be readily prepared by this method. Other useful polythioesters are those derived from the various polymethylene dithiols containing from two to ten carbon atoms and acids such as diphenoxyethane-4,4'-dicarboxylic acid, diphenoxypropane-4,4'-dicarboxylic acid, diphenoxybutane-4,4'-dicarboxylic acid, diphenoxypentane 4,4 dicarboxylic acid, diphenoxyhexane-4,4'-dicarboxylic acid, diphenylmethane 4,4-dicarboxylic acid, diphenylbutane-4,4'-dicarboxylic acid, naphthalene- 1,5 -dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-d1- carboxylic acid, 1,4-diphenoxybenzene-4,4"-dicarboxylic acid, 1,4-bis-(phenoxymethyl) benzene-4,4-dicar boxylic acid, phenoxybenzene-4,4-dicarboxylic acid, d1- phenylthioether-4,4-dicarboxylic acid and diphenyl-4,4'- dicarboxylic acid.

A particularly important and valuable application of the invention is in the production of linear polymers of high molecular weight. According to the present invention, a polythioester of low or moderate weight having mercapto end-groups can be converted within a relatively short period of time to a polymer of high molecular weight. Polymers having a mercapto group on one end and a hydroxyl or amino group on the other end can also be used.

Various methods are available for preparing low polymers containing mercapto groups. For example, a dicarboxylic acid chloride can be reacted with more than an equivalent proportion of a dimercaptan or mercaptoalcohol. Small excesses produce larger polymer molecules while large excesses produce smaller molecules. The particular method for forming the intermediate" mercapto polymer is not part of the present invention, which is directed to the interlinking of such polymers, however formed.

In order to produce polymers of high molecular weight or superpolymers, the number of mercapto, hydroxyl and amino groups and the acylating groups arising from the N-acyl polyimide interlinking agent must be approximately equal. When the functionality of the intermediate polyester is the same as that of the polyimide, as in the preparation of linear polymers, this will involve equimolecular proportions. If the average molecular weight of the intermediate polymer and the number of mercapto, hydroxyl and amino groups per molecule are known, the approximate amount of interlinking agent can be calculated. In practice, however, it is frequently desirable to establish the optimum amount of interlinking agent by empirical methods. Because of the difference in size of the molecules of intermediate polymer and interlinking agent, the proportion by weight of the interlinking agent will be relatively small.

The interlinking agent may be charged into a reactor containing well-stirred molten polymer and the reaction continued at temperatures above the melting point of the polymer. pleted, the liberated imide may be removed under reduced pressure and the resultant superpolymer removed by any suitable means. Alternatively, the interlinking agent may be added portionwise with complete reaction before the next addition. In this method, the addition of an amount of N-acyl polyimide in excess of the calculated amount will not be harmful providing the molecular weight of the polymer at the end of the previous reaction period was sufficiently high to give the desired properties. An excellent method of carrying out the reaction is to add the N-acyl polyimide or its solution to a solution of the polymer in a nonreactive solvent. Under these conditions, thorough mixing is assured. The reaction can be completed at an elevated temperature. The polymer may be recovered either by distillation of the solvent or by precipitation of the polymer in a nonsolvent.

Cross-linked polymers having properties similar to those of a vulcanized rubber or a gelled or thermoset resin can be prepared by the process of the invention when either or both the N-acyl polyimide and the intertermediate polymer contain more than two functional groups. For example, such products result when a linear polythioester having mercapto end groups is treated with an N-acyl polyimide compound having three or more lactum groups per molecule. paring cross-linked or network polymers is by reacting a nonlinear polythioester containing more than two mercapto groups per molecule with an N-acyl polyimide containing at least two imido groups per molecule.

Thus, the invention includes the conversion of thermo- After the initial reactions have been com- Another method for preplastic polymers having a mercapto group and at least one radical selected from the group consisting of mercapto, hydroxyl and amino groups per molecule to vulcanized or thermoset compositions through treatment with polyimide compounds as described above. If the initial polymer molecules contain only two reactive groups per molecule, as in the case of linear polymers terminated with mercapto groups, a polyimide compound containing at least three lactum groups must be used in order to achieve cross-linking. If the number of available mercapto, hydroxyl and amino groups per molecule is three or greater, either the bisor higher polyimide compounds may be used.

The practice of the invention is illustrated by the following representative example.

Example A low molecular weight pentarnethylene dithiolsebacate polymer was prepared by reacting 2.997 grams of pentamethylene dithiol (0.0220 mol) with 4.816 grams of sebacyl chloride (0.0201 mol) in o-dichlorobenzene solution. The reactants were heated at about 76 C. with nitrogen stirring for one hour. After standing overnight, the clear solution was heated at reflux for four hours. There was no noticeable evolution of hydrogen chloride after two and a half hours. The solvent was distilled otf and the residual melt was heated in vacuo at about 197 C. for half an hour to remove traces of hydrogen chloride and solvent. The resultant polymer had a melt viscosity of 3.05 poises at 197 C. A 2% loss of mercaptan during polymerization was assumed due to volatilization. Thus the residual excess of mercapto groups in the polymer was 0.0015 mol or 0.0030 equivalent. The total weight of polymer was 6.077 grams (0.020l)(302). where 0.0201 is the mols of non-volatile acid chloride and 302 is the weight of the polymer unit. Thus the mols of excess mercapto groups per gram of polymer equals or 0.00024. On the basis of these calculations, 4.117 grams of low molecular weight polymer containing 0.00098 mol of reactive mercapto groups were reacted with 0.450 gram of sebacyl-bis-N-phthalimide (mol. wt.=460) by heating them at reflux temperature in 15 cubic centimeters of o-dichlorobenzene for one and a half hours. This solvent was then distilled off. The residual melt, which was very fluid, slowly thickened on further reaction in the melt at about 200 C. After two hours heating, the polymer had a melt viscosity of 1213 poises at 197 C.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invent1on.

We claim:

1. A method for increasing the molecular weight of a linear polythioester having mercapto end-groups which comprises reacting said polythio ester with a polyimide in which at least 2 imido radicals are linked through their nitrogen atoms by an acyl radical of a polycarboxylic acid, each of the carbonyl groups of the acyl radical being thus attached to an imido radical and said polyimide being free from reactive substituents.

2. A method according to claim 1 in which the polyimide is used in amount equivalent to the mercapto groups in the polymer.

3. A method according to claim 2 in which the polyimide is an N,Nacyl bis imide of a dicarboxylic acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,510,567 Flory June 6, 1950 2,558,675 Flory June 26, 1951 2,594,145 Flory Apr. 22, 1952 

1. A METHOD FOR INCREASING THE MOLECULAR WEIGHT OF A LINEAR POLYTHIOESTER HAVING MARCAPTO END-GROUPS WHICH COMPRISES REACTING SAID POLYTHIO ESTER WITH A POLYIMIDE IN WHICH AT LEAST 2 IMIDO RADICALS ARE LINKED THROUGH THEIR NITROGEN ATOMS BY AN ACYL RADICAL OF A POLYCARBOXYLIC ACID, EACH OF THE CARBONYL GROUPS OF THE ACYL RADICAL BEING THUS ATTACHED TO AN IMIDO RADICAL AND SAID POLYIMIDE BEING FREE FROM REACTIVE SUBSTITUENTS. 